From: Dan Nelson
Date: May 7 2005 4:08am
Subject: Re: MySQL not using optimum disk throughput.
List-Archive: http://lists.mysql.com/mysql/183744
Message-Id: <20050507040851.GC99039@dan.emsphone.com>
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In the last episode (May 06), Kevin Burton said:
> We have a few of DBs which aren't using disk IO to optimum capacity.
>
> They're running at a load of 1.5 or so with a high workload of
> pending queries.
>
> When I do iostat I'm not noticing much IO :
>
> Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
> sda 0.00 13.73 128.43 252.94 1027.45 1695.10 513.73 847.55 7.14 90.13 285.00 2.53 96.57
>
> This is only seeing about 500k -> 1M per second throughput.
>
> When I run bonnie++ on these drives they're showing 20M->40M throughput.
>
> They're running on a RAID5 disk on XFS.
An OLTP database is not a system that requires throughput. It requires
lots of random access. MB/sec doesn't matter a bit. Instead, take a
look at the r/s and w/r columns. You're doing ~380 IOs/sec, which
sounds like maybe a 3-disk set? Each disk you add to the set should
give you another 120 or IOs per second. When you max out the number of
drives in your case, you will realize why drive manufacturers sell 15K
rpm disks: an array of 15k drives will give you double the transaction
rate (250 IO/s instead of 120) of the same number of 7200 rpm drives :)
--
Dan Nelson
dnelson@stripped